To conserve power while a computer system is temporarily idle without requiring a user to completely shut down the system, many computer systems presently employ one or more suspend modes. Such a suspend mode provides a mechanism for removing power from certain system components and later returning power to those system components without requiring a complete and possibly time consuming reboot of the system.
To implement some suspend modes, it is necessary to continue to supply power to certain system components or portions of certain system components while in suspend. For example, when the system state is stored in the system's dynamic random access memory (DRAM) during suspend (suspend to DRAM), a portion of the DRAM controller, commonly referred to as the resume well, must remain powered in order to refresh the DRAM. To prevent corruption of the DRAM contents when resuming from a suspend to DRAM mode, the circuitry in the resume well is not reset.
However, it is desirable to use the same DRAM controller in a system that additionally or alternatively supports a suspend mode that requires a resume sequence during which the resume well circuitry is reset. For example, if the system state is stored in nonvolatile memory, such as a hard disk, during suspend (suspend to disk), the DRAM and the entire DRAM controller, including the resume well circuitry, can be powered down. In that case, the resume well circuitry must be reset as part of the resume sequence.
A prior approach to using the same DRAM controller to support a suspend to DRAM mode and a suspend to disk mode requires the addition of a pin or other terminal to the DRAM controller for receiving a signal to indicate when the resume well circuitry must be reset. If the DRAM controller is a pad limited integrated circuit (IC), i.e. its minimum die size is constrained by the number of terminal pads, the addition of a terminal will increase die cost. Furthermore, the addition of a terminal to an IC, whether the IC is pad limited or not, often results in a significant increase in package cost and size because the commonly available IC packages have standard, inflexible numbers of terminals.
Therefore, the prior approach to supporting two suspend modes with the same IC by adding a terminal to the IC to receive a reset signal can increase cost and package size two of the major factors in determining IC marketability. A method and apparatus for generating a reset signal within the IC as part of an alternative approach is desired.